Evidence for a magnetospheric effect on mid‐latitude electric fields

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Abstract
Electric field measurements at Millstone Hill, which is located at a geographic latitude of 42.6°N and a geomagnetic latitude of 54.1°N, have been made during a time of extremely quiet geomagnetic activity in the 1800–0100 LT interval. The measured north‐south electric field component was primarily southward (eastward F region drift) in this data set, whereas in previously published Millstone Hill data it was northward (westward drift). Furthermore, the quiet time data are in agreement with incoherent scatter and barium cloud results at similar geographic latitudes in the European sector which are at lower geomagnetic latitudes. We thus conclude that the electrical structure over Millstone Hill is almost always affected by magnetospheric effects and that only under very quiet conditions is the classical neutral wind dynamo evident. Several mechanisms for producing the magnetospheric effect are discussed.